Sustainable metal-free leather manufacture via synergistic effects of triazine derivative and vegetable tannins

Abstract

Restrictions on heavy metals, especially chromium, have encouraged alternative tanning systems that can reduce environmental and human health risks from conventional chrome-based tanning. In this work, metal-free combination tanning was developed by using vegetable tannins and a triazine-based syntan containing active chlorine groups (SACC). Specifically, the relationship between leather performance (e.g., hydrothermal stability and organoleptic properties) and technical protocols (e.g., types and dose of tannins) was systematically established. The optimized protocol involving a unique procedure (i.e., 10% SACC pre-tanning, shaving, and 25% wattle tanning) endowed the leather with high shrinkage temperature (~ 92 °C) and met the Chinese standards for shoe upper leather (QB/T 1873-2010). Our method not only produces zero chrome-containing solid wastes, but also uses ~ 75% less tannin for leather manufacture. The excellent leather performance was ascribed to the synergistic effects, where SACC and wattle diffused into collagen fibrils and may bind to collagen via covalent, hydrogen and ionic bonding, locking the hierarchical structure of collagen from microfibrils to fiber bundles. Moreover, we summarized these findings and proposed a diffusion-binding-locking mechanism, providing new insights for current tanning theory. Together with the biodegradable spent tanning liquor, this approach will underpin the development of sustainable leather manufacture. Graphical Abstract

Reduction of Water Consumption in Leather Processing and an Investigation of the Leather Quality

“…However, only 60-70% of initial chromium is absorbed by the pelt and the remaining chromium species is released as complex industrial effluent which needs to be treated before discharging into the environment [10]. A good number of studies have been carried out by different research groups in recent years on leather tanning processes [11][12][13][14][15]. However, to the best of our knowledge, none of those studies addressed the issue of the large influx of water consumption in the leather processing system [11][12][13][14][15].…”

“…A good number of studies have been carried out by different research groups in recent years on leather tanning processes [11][12][13][14][15]. However, to the best of our knowledge, none of those studies addressed the issue of the large influx of water consumption in the leather processing system [11][12][13][14][15]. Currently, the treatment of wastewater generated from various tanneries has become a major concern for environmental pollution [16].…”

Insights into the Development of Dyeing-Assisting Amphoteric Acrylic Retanning/Fatliquoring Agents for Ecological Chrome-Free Tanned Leather Production

“…2,4,5 Aiming at chrome-free tanning, the difficult challenge is to develop the wet finishing materials i.e., retanning agents, fatliquors, and dyes, suitable for the posttanning process. 6,7 Typically, the non-chrome metal tanned leather by high oxidized starch aluminum−zirconium salts named HOS-AZ would exhibit inferior sensory properties (e.g., softness) if treated with conventional anionic wet finishing agents. This is mainly attributed to the high electropositivity of tanned leather, resulting in uneven binding of anionic materials.…”

“…Leather making is a comprehensive and complicated process that converts perishable hides and skins, actually the waste from the meat processing industry, into durable leather products . Chrome tanning, as the most important procedure of leather manufacturing, has been dominant since its industrial application in 1885. , However, due to increasingly strict regulations and limitations on Cr­(VI) (≤3 mg/kg) in leathers, chrome-free tanned products are becoming more and more popular globally. ,, Aiming at chrome-free tanning, the difficult challenge is to develop the wet finishing materials i.e., retanning agents, fatliquors, and dyes, suitable for the post-tanning process. , Typically, the non-chrome metal tanned leather by high oxidized starch aluminum–zirconium salts named HOS-AZ would exhibit inferior sensory properties (e.g., softness) if treated with conventional anionic wet finishing agents. This is mainly attributed to the high electropositivity of tanned leather, resulting in uneven binding of anionic materials .…”

Greener Solvent Assistant Dyeing: Harnessing Ionic Liquids for Eco-Friendly Tone-in-Tone Dyeing on All Leather Types

“…Wei et al reported on the use of pADD-DMENA amphoteric polymers as retanning agents, which exhibited a uniformly bright-yellow surface and demonstrated superior lightfastness, durability, and washability. Similarly, Ding et al reported on the utilization of a biomass-derived aldehyde tanning agent (BAT-iDP) in leather processing, , leading to in situ dyeing properties. A β-cyclodextrin-based tanning agent was also identified as a potent and environmentally friendly alternative to chromium-based tanning agents .…”